Method of and device for producing light metal castings, in particular parts of magnesium or mangnesium alloys

ABSTRACT

Production of light metal castings composed of magnesium or magnesium alloys, includes supplying a liquid metal first to a dosing chamber; pumping gas under pressure into the dosing chamber so as to press the liquid metal into a preliminarily evacuated mold nest; performing a production process within a system which is pressure-tightly closed from outside; performing heating of the liquid metal in a lower part of a melting device which adjoins a feed system; performing overheating of the liquid metal from a melting condition with a temperature of approximately 630° C. to a rigidification condition at a tool side to a lower region of a valve seat; and supplying and withdrawing a protective gas by a differential pressure system.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method for producing lightmetal castings, in particular for producing light metal parts ofmagnesium or magnesium alloys, as well as to a device for performing themethod.

[0002] The German patent document DE-OS 44 31 865 discloses a method ofand a device for producing pressure castings, with which in particularpressure castings of magnesium alloys can be produced. For this purposethe liquid metal is first supplied to a dosing chamber, to which a gasunder pressure is supplied as well. Subsequently, the liquid metal ispressed by the pressure gas into a mold nest which before was evacuated.The disadvantage of this method and device for performing the method isthat the pneumatic pressure conditions are not suitable for a productionfrom prototypes to the quantities of a series. In the arrangementpractically temperature conditions between the tool and the smelter arenot provided. The required temperature differences between the smelterand the feed region are too high and thereby are realizable only withconsiderable technical expenses. In particular, overheating of thesealing element takes place. The open container described in this Germanreference is not suitable for production of light metal castings overthe range from a prototype to the quantities of a series, since theprotective gas enclosure, in particular with the argon can not be built.The post-dosing of a liquid metal required for a series manufacture isalso not possible with this solution. The heating elements which areintegrated in the smelter in this reference, such as for example heatingcartridges can not provide the required rigidification of the metalmelt.

SUMMARY OF THE INVENTION

[0003] Accordingly, it is an object of the present invention to providea method of and a device of for production of light metal castings,which avoids the disadvantages of the prior art.

[0004] More particularly, it is an object of the present invention toprovide a method of and a device for production light metal castings,which provide a practical, functional manufacture of light metalcastings with low technical expense.

[0005] In keeping with these objects and with others which will becomeapparent hereinafter, one feature of present invention resides, brieflystated, in a method of production of light metal castings, whichincludes supplying a liquid metal first to a dosing chamber; pumping gasunder pressure into the dosing chamber so as to press the liquid metalinto a preliminarily evacuated mold nest; performing a productionprocess within a system which is pressure-tightly closed from outside;performing heating of the liquid metal in a lower part of a meltingdevice which adjoins a feed system; performing overheating of the liquidmetal from a melting condition with a temperature of approximately 630°C. to a rigidification condition from a tool side to a lower region of avalve seat; and supplying and withdrawing a protective gas by adifferential pressure system.

[0006] In accordance with still a further feature of the presentinvention, a device for producing light metal castings is proposed,which has a melting unit having a container; a metal supply conduitarranged in said container and extending outwardly in a pressure tightmanner; a pre-melting oven; a check valve through which the liquid metalis supplied from the pre-melting oven; a differential pressure systemwith which the container of the melting unit is connected; and sluicemeans introduced into the container of the melting means in a pressuretight manner.

[0007] When the method is performed and the device is designed inaccordance with the present invention it eliminates the disadvantages ofthe prior art.

[0008] The novel features which are considered as characteristic for thepresent invention are set forth in particular in the appended claims.The invention itself, however, both as to its construction and itsmethod of operation, together with additional objects and advantagesthereof, will be best understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a view schematically showing a device for producinglight metal castings in accordance with the present invention, whichoperates in accordance with the inventive method;

[0010]FIG. 2 is a view schematically showing an arrangement of a castingretort as a first variant inside a casting components group; and

[0011]FIG. 3 is a view schematically showing a second variant of thedesign of the casting mold and a differential pressure system of theinventive device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012]FIG. 1 shows a device for producing light metal castings inaccordance with the present invention. It corresponds to a principledesign of a system for producing light metal castings, which ispressure-tightly closed from outside. The metal which is used forproducing the light metal castings, such as for example magnesium ormagnesium alloys is heated in a casting retort 1 by heating means 2 inaccordance with the present invention, to approximately 630° C.

[0013] The shaping of the casting retort 1 is formed so that it reducestoward a feed system 4. In the lower region toward the feed system 4 theheating means 2 is arranged around the casting retort 1. The shape ofthe casting retort 1 and the arrangement of the heating means 2 in itslower regions makes possible the production of the required temperatureconditions for the melting and feeding process. Because of the conicalshape of the casting retort 1 and its arrangement on a base body 5, therequired distance and the withdrawal of the heat energy forrigidification of the material is realized.

[0014] The heating means 10 can be formed as resistance heating,infrared heating, or induction heating. The narrowing structure of thecasting retort 1 is placed on the base support 5. The outlet 5 of thecasting retort 1 is located therefore flush over an opening in the basesupport 5 and is closed by a valve unit 3. A casting mold 19 is arrangedunder the base support 5 so that it is movable vertically and in ahorizontal plane. It is connected with an evacuating device 20. Afterthe evacuation the valve unit 3 is removed by a valve control 12 via amechanical connecting member 13 from the opening, and the supply ofliquid metal into the mold nest of the casting mold 19 is released. Thesupply of the liquid metal, in particular for post-dosing during themanufacture of serial light metal castings to the casting retort 1 isperformed via a metal supply 18 from a pre-melting oven 16.

[0015] A check valve 17 prevents a return flow of liquid metal as wellas pressure equalizaiton. The check valve 17 can be arranged inconnection with the metal supply conduit 18 inside the pre-melting oven16 or in connection with the metal supply conduit 18 inside the castingretort 1. The arrangement of the check valve 17 inside the castingretort 1 provides for the advantage of pressure freedom in the metalsupply conduit 18. Gas supply is performed inside the closed systemthrough a protective gas supply conduit 18 by a pressure intensifier 9.The pressure intensifier 9 supplies a protective gas and then withdrawsit after the manufacturing process.

[0016] A control unit is arranged on the protective gas supply conduit 8and serves for providing a constant pressure. Eventually occurringpressure losses due to gas losses at untight locations are compensatedby a protective gas post-dosing 10, for example a protecting gasenvelope. The valve control 12 is formed as a pneumatic or hydrauliccontrol. A “sudden” (short-term) opening of the valve unit 3 act througha valve lock 14 and thereby prevent a pore formation of the material ofthe light metal casings.

[0017]FIG. 2 shows a schematical arrangement of a first variant of thecasting component group. In the melting device formed as the castingretort 1, the heating means 20 is arranged around the lower narrowingpart. The valve unit 3 closes the opening at outlet part of the castingretort 1 to the casting mold 19. After the performed evacuation by theevacuation device 20 the short term opening of the valve unit 3 isperformed through the valve control 12 and the valve lock 14. Therebythe liquid metal flows into the casting mold 19. During the expansion ofthe metal quantity for each part to be cast, because of the metal lossesin the casting retort 1, a multiple of the metal quantity of the part isrequired. After the supply of the liquid metal into the feed system 4the rigidification process is performed by the withdrawal of the thermalenergy through the base support5 and the automatic withdrawal of thecasting mold 19 from the feed system 4. The casting retort 1 inside thecasting component group is surrounded by a thermal insulation 6. Theavailable melting temperature is detected by the temperature sensor 7and the corresponding signal is supplied to the valve control 12.

[0018]FIG. 3 shows a second variant of the design of the casting moldand the differential pressure system of the inventive device. In thisvariant the casting retort 1 has a cylindrical shape. The heating means2 is arranged around the lower cylindrical part of the casting retort 1.The required heat difference for the rigidification process between thefeed system 4 and the casting mold 19 is provided by the thermalinsulation 6 and the withdrawal of the casting mold 19 after the supplyof the liquid metal. The supply of the protective gas is performed inthis variant by a differential pressure system. It is composed of aknown blow storage 21 and a pump system 22 for supply and withdrawal ofthe protective gas.

[0019] It will be understood that each of the elements described above,or two or more together, may also find a useful application in othertypes of constructions differing from the types described above.

[0020] While the invention has been illustrated and described asembodied in method of and device for producing light metal castings, inparticular parts of magnesium or magnesium alloys, it is not intended tobe limited to the details shown, since various modifications andstructural changes may be made without departing in any way from thespirit of the present invention.

[0021] Without further analysis, the foregoing will so fully reveal thegist of the present invention that others can, by applying currentknowledge, readily adapt it for various applications without omittingfeatures that, from the standpoint of prior art, fairly constituteessential characteristics of the generic or specific aspects of thisinvention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. A method of producing light metalcastings composed of magnesium or magnesium alloys, comprising the stepsof supplying a liquid metal first to a dosing chamber; pumping gas underpressure into the dosing chamber so as to press the liquid metal into apreliminarily evacuated mold nest; performing a production processwithin a system which is pressure-tightly closed from outside;performing heating of the liquid metal in a lower part of a meltingdevice which adjoins a feed system; performing overheating of the liquidmetal from a melting condition with a temperature of approximately 630°C. to a rigidification condition at a tool side to a lower region of avalve seat; and supplying and withdrawing a protective gas by adifferential pressure system.
 2. A method as defined in claim 1; andfurther comprising performing, within the closed system a post-dosing ofrigid light metal by a sluice device under an available pressuredifference between outer atmosphere and an inner pressure in the meltingdevice.
 3. A method as defined in claim 1; and further comprisingsupplying the light metal selectively in a liquid form through a metalsupply conduit and/or as a rigid light metal through a sluice device. 4.A method as defined in claim 1; and further comprising selecting aquantity of the light metal to be supplied as a multiple of a lightmetal quantity required for a light metal casting to be produced.
 5. Amethod as defined in claim 1; and further comprising rigidifiying theliquid light metal by a movement of a tool device away.
 6. A method asdefined in claim 1; and further comprising supplying and withdrawing ofthe protective gas through a pressure intensifier, and compensatingpressure losses by protective gas post-dosing.
 7. A method as defined inclaim 1; and further comprising performing the rigidification of thelight metal by lifting a casting retort and thereafter placing thecasting retort on a tool device of a last workpiece to be treated.
 8. Adevice for producing light metal castings of magnesium or magnesiumalloys, comprising a melting unit having a container; a metal supplyconduit arranged in said container and extending outwardly in a pressuretight manner; a pre-melting oven; a check valve through which the liquidmetal is supplied from said pre-melting oven; a differential pressuresystem with which said container of said melting unit is connected; andsluice means introduced into said container of said melting means in apressure tight manner.
 9. A device as defined in claim 8, wherein saiddifferential pressure system includes a pressure intensifier, and aprotective gas-post-dosing means arranged after said pressureintensifier and compensating pressure losses.
 10. A device as defined inclaim 8, wherein said differential pressure system includes a blowstorage and a pump system associated with the latter.
 11. A device asdefined in claim 1; and further comprising a casting retort whichnarrows in direction toward a feed system, said metal supply conduitbeing arranged in a pressure-tight manner in said casting retort andsupplying a liquid metal from said pre-melting oven through said checkvalve, said casting retort being connected with a pressure intensifier,and said pressure intensifier being connected with a protective gasdosing means which compensate pressure losses, said sluice means beingarranged in said casting retort in a pressure tight manner for supplyinga rigid light metal; a valve control means for controlling the supply ofthe liquid metal and associated with a valve lock for performing asupply in a very short time.
 12. A device as defined in claim 8; andfurther comprising a system selected from the group consisting of apneumatic system, a hydraulic system and both, and providing a valvecontrol means, said valve control means being connected with a valvelock selected from the group consisting of a hydraulic valve lock, apneumatic valve lock, and an electromechanical valve lock.
 13. A deviceas defined in claim 8; and further comprising means for rigidificationof the liquid metal by a heat-insulating, cooled supply; and aheat-insulating layer locked between said melting device and a tooldevice.
 14. A device as defined in claim 8, wherein said check valve islocated inside said container of said melting device.